1. Field of the Invention
This invention relates generally to cardiac stimulation devices, and more particularly to apparatus for connecting a cardiac lead to a cardiac stimulator, such as a pacemaker or defibrillator.
2. Description of the Related Art
The course of treatment indicated for patients suffering from cardiac arrhythmia normally depends on a number of factors, such as the age of the patient, the type and severity of the arrhythmia, as well as other factors. Many patients may be successfully treated using drug therapy, surgical intervention, or a combination of the two. However, for some patients, the best course of treatment involves direct electrical stimulation of the affected area of the heart by means of an implanted cardiac stimulator.
Conventional implantable cardiac stimulator systems typically consist of a cardiac stimulator and one or more elongated leads. The cardiac stimulator may be a pacemaker, a defibrillator, a sensing instrument, or some combination thereof. The circuitry, batteries, and other components of the cardiac stimulator are ordinarily encased within a metallic housing commonly referred to as a "can." Most of the circuitry of the cardiac stimulator is mounted on a small electronic circuit board commonly known as a multi-chip module or hybrid microcircuit.
The proximal ends of the leads of the cardiac stimulator system are connected physically and electrically to the cardiac stimulator can via a structure commonly known as a header. The distal end of each lead is implanted near the site requiring electrical stimulation or sensing. The leads function to carry electrical stimulation signals from the cardiac stimulator can to the targeted tissue and to transmit sensing signals from the targeted tissue back to the cardiac stimulator can.
A typical header consists of a molded plastic or epoxy structure that encases one or more conductor wires emanating from the cardiac stimulator can. The header also includes one or more longitudinally disposed bores that are dimensioned to receive the proximal ends of the cardiac leads. One or more electrical contacts are provided inside the header and connected to the conductor wires of the header. The contacts are positioned near or around the bore to contact the metallic parts of the proximal ends of the leads. The proximal end of each lead is retained in the header by a set screw that is tightened by the physician at the time the cardiac stimulator system is implanted or by some other retention mechanism.
In a common procedure used by physicians to implant a new cardiac stimulator system, a lead is first implanted inside the body and manipulated so that the distal end of the lead is positioned proximate the targeted tissue. The proximal end of the lead is normally left protruding from the body during the implantation procedure so that it may be readily connected to the cardiac stimulator. After the distal end of the lead has been positioned inside the body, the proximal end of the lead is connected to the header by inserting it into a bore and tightening the set screw. Following connection of the lead, the cardiac stimulator is implanted under the patient's skin.
The electrical contacts inside the header are commonly tubular in shape or are provided with tubular passages and are fabricated with inner diameters that are larger than the outer diameters of the proximal ends of the leads to provide sliding fits between the contacts and the proximal ends of the leads. A sliding fit is preferable to enable the implanting physician to insert the proximal end of the lead with minimal effort and with little risk of damaging the lead or the header. As a result of the relatively loose fit between the contacts and the proximal ends of the leads, the leads may make only intermittent electrical contact or no contact at all with the header until the set screw is tightened. Reliable electrical conduction by the lead is not ensured until the set-screw is tightened. There will normally be some time lag between the moment when the proximal end of the lead is inserted into the header and when the set screw is tightened by the physician.
Most cardiac stimulator system patients will require replacement of all or part of their cardiac stimulator systems at some point in their lifetimes. Replacement may be indicated where the cardiac stimulator has exceeded its useful life span due to battery depletion or malfunction, or where the capabilities of the cardiac stimulator no longer match the arrhythmia condition of the patient. This may occur where the patient has undergone physiological changes as a result of disease, trauma, surgery or other causes. Replacement of a typical cardiac stimulator involves surgical excision of the stimulator, disconnection of the stimulator from the cardiac lead, and connection and implantation of a replacement cardiac stimulator.
Electrical stimulation of the heart will be interrupted from the time the old cardiac stimulator is disconnected from the lead until the new cardiac stimulator is fully connected to the lead and activated. As noted above, complete connection may not be reliably achieved until the set-screw is tightened. In most cases, the duration of the interruption will depend on the skill and speed of the surgeon, and on whether the surgeon must perform any diagnostic procedures on the lead or cardiac stimulator prior to tightening the set screw.
There are several disadvantages associated with conventional lead connection systems. As noted above, the mere insertion of the proximal end of the lead into the header does not guarantee immediate electrical stimulation of the heart. In situations where the lead does not make good contact upon insertion into the header, the patient may not receive electrical stimulation from the cardiac stimulator until the set screw is tightened. Some arrhythmia patients may be adversely impacted by even short interruptions in the application of electrical stimulus to the heart, even in circumstances where the surgeon has made efforts to minimize the disconnection time.
Another disadvantage stems from the way in which conventional leads are held in place in the header. The primary mechanism for retaining the lead in the header is the set screw. Many modern cardiac stimulators have an anticipated implant life span of five years or longer. Following implantation, the connection between the cardiac stimulator and the cardiac lead is subjected to a variety of stresses that stem from the patient's physical activity and/or the rhythmic motion of the patient's breathing and heart beat. Some patients even place stress on the connection by habitually palpating their implanted cardiac stimulators with their hands. High stresses may be imparted by physical trauma to the body. Years of exposure to such stresses may loosen the set screw. In the absence of some other engaging mechanism, the lead may disconnect from the header.
The present invention is directed to overcoming, or reducing the effect of one or more of the foregoing disadvantages.